1. Field of the Invention
The present invention relates generally to an improved rear suspension system. More particularly, the invention relates to an improved rear suspension system for motorcycles which includes a progressive link mechanism which progressively increases the compression stroke of a rear wheel cushioning damper as the swing stroke of a rear wheel support member increases.
2. Description of Relevant Art
A known rear suspension system for motorcycles which absorbs and cushions a swinging motion of a rear wheel supporting member about its front end together with a rear wheel in following undulations of the road surface, which rear wheel supporting member supports the rear wheel at its rear end while the front end thereof is vertically pivotably connected to a vehicle body frame, in the form of a progressive link mechanism type rear suspension system, for example, is disclosed in U.S. Pat. No. 4,360,214 issued Nov. 23, 1982. In such progressive link mechanism type rear suspension system, a rear wheel cushioning damper is connected at one end thereof to a vehicle body frame and at the other end thereof to a rear wheel supporting member through a first link, and the body frame and the first link are interconnected through a second link. As the rear wheel supporting member swings upwardly, the damper is compressed through the first link and at the same time the first link is pivotably moved by the second link about its connection with the rear supporting member, so that the amount of pivotal movement of the first link is added to the compression stroke of the damper. In this manner, the damping force characteristic of the damper is defined as a progressive characteristic which increases in a quadratic curve-wise manner as the swing stroke of the rear wheel supporting member increases.
When turning a motorcycle, there is performed a banking operation for tilting the body in the turning direction. Therefore, for motorcycles in general, including those provided with a rear suspension system incorporating the aforesaid progressive link mechanism, it is required in designing the rear suspension system to take into consideration the arrangement of members and devices, such as a muffler and a stand, disposed on the lower surface side of the rear wheel supporting member.
In addition, required devices of the motorcycle, such as an air cleaner and a battery for example, are attached to the body. Thus, it is necessary to provide sufficient space for arrangement of such devices, and to this end it is necessary to take into consideration the positional relationship among the first and second links and the damper in order to attain a compact construction of the progressive link mechanism type rear suspension system as a whole.
Further, in order to maintain favorable driving posture characteristics of motorcycles, it is desirable that the vehicular center of gravity be set in as low a position as possible. Thus, in the aforesaid type of progressive link mechanism, it is desirable to lower the position of the center of gravity of the damper to the greatest possible extent.
The present invention provides an improved rear suspension system which effectively meets the foregoing demands.